package evaluator

Package evaluator treats the element within expression with three types, each type has its own array form:

- number

For convenience, we treat float64, int64 and so on as type of number. For example, float 100.0 is equal to int 100, but not euqal to string "100"

- string

character string quoted with `, ', or " are treated as type of string. You can convert type string to any other defined type you like by type convert functions which are mentioned later

- function or variable

character string without quotes are regarded as type of function or variable which depends on whether this function exists. For example in expression (age birthdate), both age and birthdate is unquoted. age is type of function because we have registered a function named age, while birthdate is type of variable for not found. The program will come to errors if there is neither parameter nor function named birthdate when evaluating